Protective arrangement



Dec. 30, 1930. L. F. KENNEDY PROTECTIVE ARRANGEMENT Filed Aug. 21, 1929Mfr Inventor: LuKeF. K ennedg, y

(4,440; We, Attorn e3.

Patented Dec. 30, 1930 ,UNITED;

. LUKE r. x iimrmi, or

P TE T io F1c ELECTRIC COMPANY, A CORPORATION OF NEW YORK v 'rnor'norrvnARRANGEMENT App l icatio nfil ed August 21, 1929.; Serial 1%. 387,523;

' My invention relates to improvements'in protective arrangements forelectric circuits, and more particularly forcircu-its including thewindings of electric apparatus sub- -ject to transient magnetizingcurrents and an object of my invention is to provide an improvedprotective arrangement whereby to avoid unnecessary interruptions due totr'an sient. magetizing currents and yet maintain the desired degree ofsensitivity of protection under ordinary'steady state conditions.

Whenever electric apparatus having windings subject to transientmagnetizing cur- 'rents, for example, a power-transformer,1s

connected toa source of E. M. F. due to the momentarily great intensityof this current A which may be several-times normal loadcurrent,depending on the point of the M. wave at which the circuit closureoccursand the magnetic condition of the iron, theprotective gearfrequently operates and causes the opening of the circuit unnecessarily;Va-

rious expedients have been'adopted to avoid this difliculty, :Amongthese are permanently decreasing the sensitivity ofthe protective gearor setting it to operate at a point above any expected intensity oftransientmagnetizing current and givin'gthe protectivegear a timesetting sufiiciently. great to avoid'oporation during the probablemaximum period 1 of the transient. Both these may be and oftenareobjectionable since they involve a sacrifice ofprotection under normalsteady state conditions. Otherarrangements have involved either manuallyor automatically According to my inventiomlpropose in efiect to decreasethesensitivityof the relay in accordance with a. characteristic'ofthe-transient magnetizing current which is characterized by one or moreharmonicsof which-the second is in general predominating. In this way.the time and intensity of the efiect are controlled by thevery factorcausingithe trouble.

My invention will better understood" from'the following description whenconsidered in connection with the accompanying drawing,andits scope willbe pointed out in the appended claims.

In the accompanying drawing, Fig. 1 illustrates diagrammaticaly aprotective arrangment embodying my invention, and Fig.

of'the embodiment of invention shown in the embodiment of inventionshown in Fig. 1, electricapparatus, 'subjectto transient magnetizingcurrents, such as apower transformer 5,- isarranged to have the'circultof its'primaryand secondary windings.

6 and 7 controlled so as to be connected to a source of E. M. F., notshown, by suitable circuit interrupting means illustrated as a latchclosed circuit breaker 8;having,a trip'coil 9.

For controlling the circuit breaker 8'1 through its trip coil,"I haveshownmeans, including a relay 10, which is arranged to con trol contacts11 in circuit with the trip coil and which according to my invention ispro vided with means for'restraining the opera, ltion of the relayconnected to 'be energized only'qin accordance withi a predeterminedharmonic of the transient magnetizing current ofthe transformer 5. 7

disk type and includes a movable member such' asthe disk'12 with whichare inductively associated electromagnetic means, such as restrainingand operating motor elements 13, 14, whose windings 15, 16 arerespectively connected to' be energized in accordance with the sum ofand the difference between the currents in'the windings 6 and 7 of thetransformer 5. For this purpose the: re-

straining winding 15 may be connected in series in a protective circuitincludng the secondaries of current; transformers 17 and 18 connected inseries for normally circulating current while the operating winding 16is connected across points 19 and 20 in' As shown,-the relay '10 is ofthe induction PHILADELPHIA, PENNSYLVANIA, Assrdnon T0. GENERAL 2illustrates diagrammatically a modification In order to avoid this thiscircuit normally at the same potential, the current transformers 17 and18 being connected in the circuits of the power transformer windings 6and 7 respectively. The motoring elements 18, 14 are arranged to ex erton the disk 12 opposing torques whose respective directions areindicated by the arrows 3, 4. The ratio of these torques may of coursebe any desired value which can be governed, for example, by the relativenumber of turns in the windings 15 and 16.

In accordance with my invention, I provide an additional restraint whichis effective during the transient magnetizing current perod. As shown inFig. 1 this may be ac complished by providing a circuit tuned to aharmonic of the magnetizing current such for example as the secondharmonic. For this purpose a condenser 21 may be connected across apart, such as a half. of the restraining winding 15 and tuned therewithto form a parallel resonant circuit for such harmonic. If the powertransformer 5 is subject to energization from eitherside then a furtherresonant circuit including the condenser 22 and the other half of therestraining winding 15 may be provided. 7

If two parallel resonant circuits are thus provided there is theprobability of transformer action between the two halves of therestrainingwinding when energized by the selected harmonic of thetransient magnetizing currentwith the possibility of the additionalrestraint being more or less nullified. I may provide the relay 10, asshown in Fig. 2, with two independent electromagnetic restrainingelements 23, 24, having windings 25, 26 arranged in seriesresonantcircuits tuned to the second harmonic of the transientmagnetizing current. As shown, these circuits include the condensers 27,28, and are connected across the secondaries of the current transformers17, 18, respectively. These restraining elements may operate for exampleon a second disk12 secured to the same shaft as the disk 12 on which themain restraining and operating elements 13 and 14: operate. IVith thisarrangement one or the other of the harmonic restraining elements 23,24, depending on which winding of the transformer is initially excited,will exert a restraining torque assisting the torque of the restrainingelement 13, and proportional to the second harmonic of the transientmagnetizing current in the associated power transformer winding.Inasmuch as the additional restraint is substantially dependent on theexistence of the second harmonic which occurs only during the transientmagnetizing pe riod, this restraint does not affect the sensitivity ofthe relay 10 so that it can function with the usual sensitivity underthe ordinary steady state conditions.

\Yhile Iliave shown and described my invention in considerable detail, Ido not desire to be limited to the exact arrangements shown, but seek tocover in the appended claims all those modifications that fall withinthe true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is 1. In combination with an electric apparatus having windingssubject to transient magnetizing currents and a circuit interrupter forcontrolling't-he circuit of said windings, means for controlling saidinterrupter ineluding a differential relay having a movable member,restraining and operating means for controlling the movement thereofrespectively connected to be energized in accordance with the sum of andthe diiference between the currents of said windings, and means foradditionally restraining the movement of said member only in accordancewith the second harmonic of the transient magnetizing current of saidapparatus.

2. In combination with an electric apparatus having a winding subject totransient magnetizing currents, and a circuit interrupt er controllingthe circuit of said winding, means for controlling said interrupterincluding a relay having a restraining winding circuit tuned to apredetermined harmonic of the transient magnetizing current of said.

apparatus.

8. In combination with an electric apparatus having a winding subject totransient magnetizing currents and a circuit interrupter for controllingthe circuit of said winding, means including a relay for controllingsaid interrupter, means for restraining the operation of said relayconnected to be energized only in accordance with a predeterminedharmonic of the transient magnetizing current of said apparatus.

4. In combination with an electric apparatus having a winding subject totransient magnetizing currents and a circuit interrupter for controllingthe circuit of said winding, means for controlling said interrupterincluding a relay having a movable member, operating and restrainingmeans for controlling the movement thereof and means for additionallyrestraining the movement of said member only in accordance with apredetermined harmonic of the transient magnetizing current of saidapparatus.

5. In combination, a power transformer, a circuit interruptercontrolling the circuit thereof, means for controlling said interrupterincluding a differential relay having a movable member, restraining andop erating means for controlling the movement thereof respectivelyconnected to be energized in accordance with the sum of and thedifference between the currents in the primary and secondary windings ofsaid transformer and means for additionally restraining the movement ofsaid member including a restraining winding circuit tuned to the secondharmonic of the {transient magnetizing current of the transformer;

6. In combination with a power transformer, a circuit interrupter forcontrollin the circuit thereof, meansfor controlling sai interrupterincluding'a relay having a movable induction disk means, electromagneticmeans inductivelyassociated with said disk means" and arranged 'toexertopposing torques thereon, and means for increasing the effect of one ofsaid torques only in response to the second harmonic of the transientmag netizing current of the transformer.

7. In combination with electric apparatus having a winding subject totransient magnetizing' currents," and a circuit interruptercontrollingthe circuit of said winding, means for controlllng saidinterrupter. including a relay having a movable member andelectromagnetic'means arranged to exert opposing torques on said member,and means fOIlIlcreasingthe effect of one of said torques'only inresponse to a predetermined harmonic of the transient magnetizingcurrent of said ap- I 1 paratus.

8. In combination with a power transformer and a circuit interrupter forcontrolling the. circuit thereof, means for controlling said interrupterincluding a relay having restraining and operating elements respectlvely connected tobe energized in accordance with the sum of andthe difference 7 between the currents in the primary and secondarywindings of the transformer [and means for exerting an additionalrestraining effect connected to be energized in accordance with apredetermined harmonic of the transient magnetizing current of thetransformer. V

9. In combination with a power transformer and a circuitinterrupter forcontrol- I ling the circuit thereof, means for controlling saidinterrupter including a relay having restraining and operatingwindingsrespectively connected to be energized in accordance with the sum of andthe difierence between the currents in the primary and secondarywindings of the transformer and means for exerting an additionalrestraining effect connected to be energized in accordance with thesecond harmonic of the transient magnetizing current of the transformer.

10. In combination with electric apparatus having a Winding subject totransient magnetizing currents and a circuit interrupter for controllingthe circuit of said winding, means for controlling said interrupterincluding a relay and means responsive to a' characteristic of thetransient magnetizing current otherthan the fundamental thereof forpreventing operation of the relay.

In Witness whereof, I have hereunto set my hand this 17th day of August,1929.

LUKE F. KENNEDY.

